The life cycle of the cellular slime mold Dictyoselium discoideum involves a vegetative stage in which amoeboid cells exist independently. Subsequently the independent cells aggregate to form a multicellular pseudoplasmodium. The cell contacts and association result in the differentiation of two cell types, prespore and prestalk cells. These cells ultimately form the mature fruiting bodies. The phenomenon of particular interest concerns the necessity of cell association in differentiation. It has been observed that isolated cells cannot differentiate into prespore cells. Studies have been conducted previously which revealed that major increases in the size of the plasma membrane globular proteins occur during aggregation. These particulate structures may provide the morphological and functiional basis for cell interactions which affect cell division, adhesion and differentiation. The proposed research involves the use of morphogenetic blocking agents such as concanavalin A and specific antiserum known to bind to cell surfaces. Certain enzymes such as papain or pronase which dissociate pseudoplasmodia will be used to determine the degree of cell contact necessary to effect cell differentiation. The effect of both cell surface "blocking" agents and enzymes will be assayed by thin-sectioning the treated cells to determine if prespore cell differentiation has occurred. In addition freeze-fracture studies of cells treated with ferritin labelled antiserum or Con A will be conducted to determine the sites at which they are bound. These experiments may yield information concerning the role of the plasma membrane particles in the development of Dictyostelium.